Shoulder impingement has been identified as the most common cause of shoulder pain in the adult general population. Sometimes therapeutic pushing on the middle part of the back (manual therapy) decreases shoulder pain in someone experiencing shoulder impingement. We do not known what causes the decreased shoulder pain. It could be that the therapeutic pushing makes things move better. It may be that the person getting their back treatment thinks they are better or the physical therapist who provides the manual treatment thinks it works.